The present invention relates generally to a method and an apparatus for feeding a material web. More specifically, the present invention relates to a method for the intermittent forward feeding of a material web, provided with transverse weakening lines, in register with the weakening lines. The present invention also relates to an arrangement for the intermittent forward feeding of a material web provided with transverse weakening lines.
In the manufacture of weblike packing material of the type which subsequently is converted into packing containers, it happens frequently that some form of processing, e.g. punching of emptying holes in the web, is to be carried out. When the material web is provided with weakening lines in the form of crease lines in a certain pattern (so as to facilitate the folding when the material is converted into packing containers) the processing has to be done in register with the crease line pattern. In other words, the emptying holes must be placed in an accurate relation to the crease line pattern. This is done by intermittent feeding of the material web past the processing tool (e.g. a hole punch). It has been found to be difficult to ensure that the web is punched each time with the crease line pattern in exactly the correct position in relation to the punching tool, since the distance between the crease lines, for natural reasons, does not exactly coincide with the length of the forward feed. Hence manual correction of the length of the forward feed becomes necessary after a certain number of forward feeds, which renders the manufacture more complicated and more expensive without providing in return the desired uniform placing of the holes.
It is known that the length of forward feed can be corrected and controlled continuously during the forward feeding with the help of a photocell which reads the length of forward feed with the help of markings, so-called photocell marks. These may be present on the web, which may consist of limited squares in contrasting colors which have been applied by printing onto the web in register with the crease line pattern. However, this system makes necessary an expensive and complicated electronic arrangement which in practice has been found not to function with the required safety. The method in many cases fails to give sufficient accuracy, since it wholly depends on the accuracy with which the photocell marks have been applied in relation to the crease line pattern.
In it an object of the present invention to provide a method and an arrangement of the type described in the introduction which are not subject to the abovementioned disadvantages.
It is a further object of the present invention to provide a method and an arrangement which work according to a simple principle and with simple mechanical components and which consequently are of high accuracy and safety in operation.
It is a further object of the present invention to provide a method and an arrangement which accept certain unavoidable faults in the distance between the crease lines and which continuously compensate for these faults so that they are not accumulated during working over long periods.
These and other objects have been achieved in accordance with the invention in that a method for the intermittent forward feeding of a material web, provided with transverse weakening lines, in register with the weakening lines the web being fed forward by a driving element over a distance which exceeds the desired length of forward feed by a defined partial distance. Thereupon the driving element is disengaged and a register-holding element, through engagement with a weakening line, restores a part of the web situated between the register-holding element and the driving element, until the weakening line has been brought into a desired position at a predetermined distance from the driving element.
An arrangement for the intermittent forward feeding of a material web provided with transverse weakening lines has a driving element capable of being disengaged and register-holding element located in front of the driving element seen in the direction of feeding of the web. The register holding element is provided with drivers co-operating with the weakening lines of the web and is adapted so that through engagement with a weakening line it moves the same to a repeatable position at a certain distance from the driving element.
Preferred embodiments of the method as well as the arrangement in accordance with the invention have been given moreover the characteristics which are evident from the description below.